A. TECHNICAL FIELD
This invention relates to the separation of petroleum refinery off-gases. More particularly, it relates to the separation of a light vapor fraction containing hydrogen and one or more C.sub.1 to C.sub.4 hydrocarbons from hydrogen-rich refinery off-gases to give a liquid product fraction.
B. PRIOR ART
The refining of petroleum, e.g., catalytic reforming of petroleum, is often accompanied by the evolution of significant volumes of off-gases composed predominantly of hydrogen together with substantial quantities of C.sub.1 to C.sub.4 hydrocarbons (i.e., methane, ethane, propanes and butanes) and gasoline. Ordinarily, such off-gases are routed to the refinery fuel gas system or simply disposed of by flaring. However, the difference between the value of off-gas components as separated and recovered liquid and their value as refinery fuel is often increased by market conditions to the point where there is economic justification for seeking their separation and recovery. For example, under current market conditions, such a difference can amount to a pretax profit of about 25 cents per gallon of C.sub.4 and heavier components recovered in the form of gasoline, plus 6 cents per gallon recovered to LPG (liquefied petroleum gas) sales.
Although numerous techniques have been developed for separating gaseous mixtures into their constituents as disclosed, for example in
U.S. Pat. No. 2,940,270 issued June 14, 1960 to D. F. Palazzo et al. for GAS SEPARATION; PA0 U.S. Pat. No. 3,026,682 issued Mar. 27, 1962 To D. F. Palazzo et al. for SEPARATION OF HYDROGEN AND METHANE; PA0 U.S. Pat. No. 3,119,677 issued Jan. 28, 1964 to J. J. Moon et al. for SEPARATION OF GASES; PA0 U.S. Pat. No. 3,255,596 issued June 14, 1966 to S. G. Greco et al. for PURIFICATION OF HYDROGEN RICH GAS; PA0 U.S. Pat. No. 3,292,380 issued Dec. 20, 1966 to R. W. Bucklin for METHOD AND EQUIPMENT FOR TREATING HYDROCARBON GASES FOR PRESSURE REDUCTION AND CONDENSATE RECOVERY; PA0 U.S. Pat. No. 3,397,138 issued Aug. 13, 1968 to K. H. Bacon for GAS SEPARATION EMPLOYING WORK EXPANSION OF FEED AND FRACTIONATOR OVERHEAD; PA0 U.S. Pat. No. 3,516,261 issued June 23, 1970 to M. L. Hoffman for GAS MIXTURE SEPARATION BY DISTILLATION WITH FEED-COLUMN HEAT EXCHANGE AND INTERMEDIATE PLURAL STAGE WORK EXPANSION OF THE FEED; PA0 U.S. Pat. No. 3,729,944 issued May 1, 1973 to C. S. Kelley et al. for SEPARATION OF GASES; PA0 U.S. Pat. No. 3,996,030 issued Dec. 7, 1976 to E. G. Scheibel for FRACTIONATION OF GASES AT LOW PRESSURE; and PA0 U.S. Pat. No. 4,040, 806 issued Aug. 9, 1977 to K. B. Kennedy for PROCESS FOR PURIFYING HYDROCARBON GAS STREAMS,
a need still exists for a way of economically separating refinery off-gases into a liquid product fraction, and a light vapor fraction containing hydrogen and one or more C.sub.1 to C.sub.4 hydrocarbons beginning at the low end under the aforementioned circumstances.
Accordingly, it is an object of the present invention to provide a means for separating petroleum refinery off-gases, e.g., catalytic reformer off-gas, into useful fractions or components.
Another object is to provide a method for separating petroleum refinery off-gases, e.g., catalytic reformer off-gas, into a liquid product fraction and a fraction containing hydrogen and one or more C.sub.1 to C.sub.4 hydrocarbons.
These and other objects of the invention as well as a fuller understanding of the advantages thereof can be had by reference to the following description, drawings and claims.